How to calculate how much sugar to use as antifreeze in drinking water?
Sea water does not freeze until about −2 °C (28 °F) if you add more salt you can lower the freeze point to -21°C.
We know from How much sea water can I safely drink? that drinking salt water is not good. But adding any substance to water that will form a solute will lower the freezing temp. You can drink as much sugar water as you want, the only risk is added calories which you likely need anyhow.
The higher the concentration of salt, the lower the freezing point drops. Any foreign substance, such as sugar, alcohol, or any chemical salt, added to the water, forms a solute, which will lower the freezing point and melt ice. Source
So if I want to add sugar to my water to keep it from freezing how do I calculate how much sugar per unit of water I need to add, to keep it liquid at a given temperature?
1 answer
This can be calculated using a property called cryoscopic constant Kf which links the concentration of a solved substance to the freezing point depression Td:
Td = m * Kf
where m is the molality which is the amount of mols of solved substance per kg of solvent (here water). For water Kf is 1.86K*kg/mol and the molar mass of sugar (sucrose) is 342g/mol. So to calculate the freezing point depression do:
Td = 1.86 / 342 * mass of sugar in g / mass of water in kg
Some examples for grams of sugar added to 1 liter water:
g/l Td 10 0.054 50 0.27 500 2.7
I found a science-fair-project that measured this.
So you need a huge amount of sugar for a small effect, not very practical.
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